The term Bus is taken from the IEEE 141, 241, and 399 standards where impedance diagrams are discussed. Impedance diagrams are used to facilitate short circuit calculations, whereby the connection point between two different impedance values is described as a bus.

Very often, a bus represents the bus bar within a piece of switchgear, MCCs, Panels or other load points, however for convenience of entry, additional buses are created between two cables, between cables and transformer so that each impedance component can be entered separately without manually calculating an equivalent impedance for a group of components.